In the electronics industry various deposition techniques have been developed wherein selected materials are deposited on a target substrate to produce electronic components such as semiconductors. One type of deposition process is chemical vapor deposition (CVD), wherein gaseous reactants are introduced into a heated processing chamber resulting in films being deposited on the desired substrate. One subtype of CVD is referred to a plasma enhanced CVD (PECVD) wherein a plasma is established in the CVD processing chamber.
Generally, all methods of deposition result in the accumulation of films and particulate materials on surfaces other than the target substrate, that is, the deposition materials also collect on the walls, tool surfaces, susceptors, and on other equipment used in the deposition process. Any material, film and the like that builds up on the walls, tool surfaces, susceptors and other equipment is considered a contaminant and may lead to defects in the electronic product component.
It is well accepted that deposition chambers, tools, and equipment must be periodically cleaned to remove unwanted contaminating deposition materials. A generally preferred method of cleaning deposition chambers, tools and equipment involves the use of perfluorinated compounds (PFC's), e.g., C2F6, CF4, C3F8, SF6, and NF3 as etchant cleaning agents. In these cleaning operations a chemically active fluorine species, which is normally carried in a process gas, converts the unwanted and contaminating residue to volatile products. Then, the volatile products are swept with the process gas from the reactor.
Ion implantation is used in integrated circuit fabrication to accurately introduce controlled amounts of dopant impurities into semiconductor wafers and is a crucial process in microelectronic/semiconductor manufacturing. In the ideal case, all feedstock molecules would be ionized and extracted, but in reality a certain amount of feedstock decomposition occurs, which results in the deposition on and contamination on the surfaces in the ion source region, or parts of the ion implanter tool, such as, low voltage insulators and the high voltage components. The known contamination residues are silicon, boron, phosphorus, germanium or arsenic. It would be a significant advance in the art of ion implantation to provide an in situ cleaning process for the effective, selective removal of unwanted residues deposited throughout the implanter, particularly in the ion source region, during implantation. Such in situ cleaning would enhance personnel safety and contribute to stable, uninterrupted operation of the implantation equipment. A gas-phase reactive halide composition, e.g., XeF2, NF3, F2, XeF6, SF6, C2F6, IFs or IF7, is introduced to the contaminated parts for sufficient time and under sufficient conditions to at least partially remove the residue from the components, and to do so in such a manner that residue is removed selectively with respect to the materials from which the components of the ion implanter are constructed.
In a micro electro mechanical system (MEMS), a mixture of sacrificial layers (usually with amorphous silicon) and protective layers, thus device structure layers, are formed. Selectively removing the sacrificial materials is a critical step for the structure release etching process, where several microns of sacrificial material need to be removed isotropically without damaging other structures. It has been understood that the etching process is a selective etching process that does not etch the protective layers. Typical sacrificial materials used in MEMS are: silicon, molybdenum, tungsten, titanium, zirconium, hafnium, vanadium, tantalum, niobium. Typical protective materials are nickel, aluminum, photoresist, silicon oxide, silicon nitride.
In order to efficiently remove the sacrificial material, the release etching utilizes an etchant gas capable of spontaneous chemical etching of the sacrificial layers, preferably isotropic etching that removes the sacrificial layers. Because the isotropic etching effect of xenon difluoride is great, xenon difluoride (XeF2) is used as the etchant for lateral etching process.
However, xenon difluoride is expensive, and is a material difficult to deal with. Xenon difluoride is unstable on contact with air, light or water vapor (moisture). All xenon fluorides must be protected from moisture, light and air to avoid formation of xenon trioxide and hydrogen fluoride. Xenon trioxide is a colorless, nonvolatile solid that's dangerously explosive. Hydrogen fluoride is not only dangerous, but also reduces efficiency of etching.
Additionally, xenon difluoride is a solid having a low vapor pressure which makes deliver of xenon difluoride to the process chamber difficult.
The following references are illustrative of processes for the deposition of films in semiconductor manufacture and the cleaning of deposition chambers, tools and equipment and the etching of substrates, the etching of sacrificial layers in a MEMS, and for the cleaning of the ion source region in an ion implantation system used in the fabrication of a microelectronic device:
U.S. Pat. No. 5,421,957 discloses a process for the low temperature cleaning of cold-wall CVD chambers. The process is carried out, in situ, under moisture free conditions. Cleaning of films of various materials such as epitaxial silicon, polysilicon, silicon nitride, silicon oxide, and refractory metals, titanium, tungsten and their silicides is effected using an etchant gas, e.g., nitrogen trifluoride, chlorine trifluoride, sulfur hexafluoride, and carbon tetrafluoride.
U.S. Pat. No. 6,051,052 discloses the anisotropic etching of a conduct material using fluorine compounds, e.g., NF3 and C2F6 as etchants in an ion-enhanced plasma. The etchants consist of a fluorine containing chemical and a noble gas selected from the group consisting of He, Ar, Xe and Kr. The substrates tested include integrated circuitry associated with a substrate. In one embodiment a titanium layer is formed over an insulative layer and in contact with the tungsten plug. Then, an aluminum-copper alloy layer is formed above the titanium layer and a titanium nitride layer formed above that.
US 2003/0047691 discloses the use of electron beam processing to etch or deposit materials or repair defects in lithography masks. In one embodiment xenon difluoride is activated by electron beam to etch tungsten and tantalum nitride.
GB 2,183,204 A discloses the use of NF3 for the in situ cleaning of CVD deposition hardware, boats, tubes, and quartz ware as well as semiconductor wafers. NF3 is introduced to a heated reactor in excess of 350° C. for a time sufficient to remove silicon nitride, polycrystalline silicon, titanium silicide, tungsten silicide, refractory metals and suicides.
Holt, J. R., et al, Comparison of the Interactions of XeF2 and F2 with Si(100)(2X1), J. Phys. Chem. B 2002, 106, 8399-8406 discloses the interaction of XeF2 with Si(100)(2X1) at 250 K and provides a comparison with F2. XeF2 was found to react rapidly and isotropically with Si at room temperature.
Chang, F. I., Gas-Phase Silicon Micromachining With Xenon Difluoride, SPIE Vol. 2641/117-127 discloses the use of XeF2 as a gas phase, room temperature, isotropic, silicon etchant and noted that it has a high selectivity for many materials used in microelectromechanical systems such as aluminum, photoresist and silicon dioxide. At page 119 it is also noted that XeF2 has a selectivity of greater that 1000:1 to silicon dioxide as a well as copper, gold, titanium-nickel alloy and acrylic when patterned on a silicon substrate.
Isaac, W. C. et al, Gas Phase Pulse Etching of Silicon For MEMS With Xenon Difluoride, 1999 IEEE, 1637-1642 discloses the use of XeF2 as an isotropic gas-phase etchant for silicon. It is reported that XeF2 has high selectivity to many metals, dielectrics and polymers in integrated circuit fabrication. The authors also note at page 1637 that XeF2 did not etch aluminum, chromium, titanium nitride, tungsten, silicon dioxide, and silicon carbide. Significant etching also had been observed for molybdenum:silicon; and titanium:silicon, respectively.
Winters, et al, The Etching of Silicon With XeF2 Vapor, Appl. Phys. Lett. 34(1) 1 Jan. 1979, 70-73 discloses the use of F atoms and CF3 radicals generated in fluorocarbon plasma induced dissociation of CF4 in etching solid silicon to produce volatile SiF4 species. The paper is directed to the use of XeF2 to etch silicon at 300 K at 1.4×10−2 Torr. Other experiments showed that XeF2 also rapidly etches molybdenum, titanium and probably tungsten. Etching of SiO2, Si3N4 and SiC was not effective with XeF2 but etching was effective in the presence of electron or ion bombardment. The authors concluded that etching of these material required not only F atoms but also radiation or high temperature.
U.S. Pat. Nos. 6,870,654 and 7,078,293 both disclose a structure release etching process by using an etchant having a fluorine group or a chroleine group to replace xenon difluoride, avoiding the difficulties resulting from using the xenon difluoride. However, the etching effect is not as efficient as the use of xenon difluoride. Therefore, U.S. Pat. Nos. 6,870,654 and 7,078,293 disclose a special structure for facilitate the structure release etching process such that the processing time etc is commensurate with that of xenon difluoride.
US20060086376 discloses the use of XeF2 for cleaning the residues (silicon, boron, phosphorus, germanium or arsenic) from the components of the ion implanter, in the fabrication of a microelectronic device.
Specifically, US20060086376 relates to the in situ removal of residue from the vacuum chamber and components contained therein by contacting the vacuum chamber and/or components with a gas-phase reactive halide composition, e.g., XeF2 for sufficient time and under sufficient conditions to at least partially remove the residue from the components, and to do so in such a manner that residue is removed selectively with respect to the materials from which the components of the ion implanter are constructed.
One of industry objectives is to find new etchants that can be used to remove difficult to remove titanium nitride (TiN) films from silicon dioxide (SiO2) and silicon nitride (SiN) coated surfaces. Theses surfaces are found in the walls of semiconductor deposition chambers, particularly quartz chambers and quartz ware, semiconductor tools and equipment. Many of the conventional fluorine based etchants that attack TiN films also attack SiO2 and SiN surfaces and, therefore, unacceptable for removing TiN deposition products from semiconductor deposition chambers and equipment.
Another industry objective is to provide a method for selective removal of silicon, from silicon dioxide (quartz) surfaces such as those commonly found in semiconductor deposition chambers and semiconductor tools, as well as devices in MEMS.
There is yet another industry objective for providing a method for generating or forming xenon difluoride on site as needed for lower cost of ownership.